Referring to FIG. 26, there is illustrated a conventional vacuum cleaner including dirt collecting chamber 141 with a bottom, and air inlet 142 provided in a side wall of dirt collecting chamber 141. A dirt-entrained air stream is tangentially introduced through air inlet 142 into dirt collecting chamber 141. Cover 144 is provided to cover upper opening 143 of dirt collecting chamber 141 and air outlet 145 is formed in cover 144. Further, there is provided filter 146 such that it covers upper opening 143 of dirt collecting chamber 141. Upon operation of the vacuum cleaner, dirt particles are suctioned from suction port 148 and collected through air inlet 142 in dirt collecting chamber 141. The collected dirt particles are centrifugally separated in dirt collecting chamber 141 and dirt-free air is exhausted through, in turn, filter 146 and air outlet 145 (see, e.g., Japanese Patent Laid-open Publication No. 2001-104223).
In such conventional arrangements, the dirt particles collected via air inlet 142 in dirt collecting chamber 141 adhere to filter 146 to occlude it, thereby resulting in deterioration of a force for suctioning the dirt particles. In order to solve the above problems, an area of filter 146 may be increased; however, the sizes of dirt collecting chamber 141 and the vacuum cleaner themselves should be increased accordingly.